As a magnetic recording medium adapted to be mounted in a hard disk drive device (HDD device), there is a magnetic disk. The magnetic disk is produced by coating a NiP film on a metal substrate made of an aluminum-magnesium alloy or the like or by laminating a magnetic layer and a protective layer on a glass substrate or a ceramic substrate. Aluminum alloy substrates have conventionally been widely used as substrates for magnetic disks. However, following the reduction in size and thickness and the increase in recording density of magnetic disks in recent years, glass substrates excellent in surface flatness and thin-plate strength as compared with the aluminum alloy substrates have started to be used.
With respect to magnetic disks formed with at least a magnetic layer on a magnetic disk glass substrate, the increase in recording density has advanced year by year and those magnetic disks having a magnetic layer containing granular particles are becoming predominant. In such a magnetic layer, it is necessary to reduce the particle size of the granular particles or enhance the crystal orientation of the granular particles in order to achieve a further increase in recording density (e.g. 160 GB or more per disk, particularly 250 GB or more per disk). In order to reduce the particle size of the granular particles or enhance the crystal orientation of the granular particles as described above, it is necessary to improve the properties of a magnetic disk glass substrate, particularly to reduce its surface roughness or reduce defects present on its surface. As a magnetic disk glass substrate with a reduced surface roughness, there is, for example, one disclosed in Patent Document 1.
In recent years, in order to achieve a further increase in recording density, there has been advanced the development of patterned media such as a discrete track medium in which adjacent tracks are magnetically isolated from each other. As a method of manufacturing such a patterned medium, there is, for example, a method of forming a magnetic layer on a glass substrate and then physically dividing this magnetic layer to thereby isolate tracks from each other. When dividing the magnetic layer, a pattern is formed on the magnetic layer using the nanoimprint technique.
In this event, if a defect (particularly a convex defect) is present on the glass substrate, the above-mentioned pattern is not formed on the magnetic layer where this defect is present. Specifically, the defect on the glass substrate is succeeded in the formation of the magnetic layer so that the defect is also formed on the magnetic layer. If the nanoimprint is carried out in this state, a pattern of a stamper is not formed only around this defect. Further, depending on circumstances, there is a possibility of damage to the stamper. Therefore, in the manufacture of a patterned medium using the nanoimprint technique, it is required that defects be extremely few on a glass substrate.